1970 429 SCJ

210 on avg

Dragkid, maybe you should pull it out, tear it down and at least do a quick cylinder hone and put some new rings and bearings in it. That will eliminate the possibility of this problem, but maybe a few other common problems as well. Its cheap insurance!

Mark Miller wrote:

BBFTorino wrote:I will assume that you have already done a compression check, and they all show within specs?

He posted Compression was between 148-151 psi but somebody said a stock 429 SCJ should be 190-200 psi?

Thats if it has the original D0AZ SCJ-Boss 429 solid cam and forged flat top pistons. I agree with BBF Torino. With a rare engine like that I would want to invest a bit of time to make sure everything is up to snuff.

Considering your low vacuum it sounds like valve timing is off. This can happen either at the cam and crank sprocket or valves being to tight. If upon acceleration it pops back through the carburetor that is most likely valves too tight. On another note make sure your crankcase isn't full of fuel from an internal leaking fuel pump. I can almost guarantee it is not a carburetor problem even though on your Holley you probably will have a problem because of a now busted power valve. It only takes one good backfire to cause it to leak. I have a 500 horsepower 460 in my 79 CVX20 jet boat and run my base timing at 14 degrees and maximum 32° at about 3,500 RPM or more. 850 double pumper Holley, HEI distributor, performer RPM intake, timing gears straight up, CP performance hydraulic cam, roller rockers, CNC ported 1968 C8VE cast iron heads with oversized stainless valves, intake and exhaust port matched to heads,10 quart pan with scraper/ windage tray. I thought it was only 475 horsepower but after talking to CP performance they said according to my 4800 RPMs and impeller size AA it had to be at least 500 horsepower. I have been a Master ASE TECHNICIAN WITH ENGINE PERFORMANCE since 1976 and have been the engine performance and carburetor specialist at most of the places I've worked at over my 56 year career. I'm also an Acura Master Tech since 1992. https://images.app.goo.gl/4LUUudx9sqnBxh256.
https://photos.app.goo.gl/kDjyxWCZpxsVtR3W6.
I forgot to say that valves to tight causes valve timing to be more advanced. Of course, too loose retards valve timing.

We you said, "When i go to shut my engine off, it tends to "diesel" and i hate that it does that." indicates that your throttle plates are too far open because you were trying to get it to idle with only 10 in vac which probably cam timing/valve adjustment. If somebody decided to put hydraulic lifees on top of the original cam would also cause this and many other problems. I have seen it happen before.

I have just read about all the trouble you are having. There have been a lot of good suggestions from members and One was the Use of an 850 Holley Double Pump Carb. Many believe that an 850 is too much but those who have used it like the member who mentioned it know how much better the Engine will run with an 850. That being said, the Engine will run with anything from a 2bbl on, yes a 2bbl if everything is right and I have a 429 factory 2bbl Manifold. I wouldn’t use it because I know the engine needs an 850. This is from more than 49 years working on Performance Engines. A 289 HiPo had a 715. How can anyone think a 600 or 750 is going to feed a Super Cobra Jet? For the non believers, Hot Rod Magazine or Car Craft did a series of Dyno Test about 30 or more years ago and showed that 351 Cleveland Engines and 429 460 Engines gained about 32 HP above 5,000 RPM with an 850.
On another note it seems that one of the most important things left out of the conversation was that you said you have 10 inches of Vacuum. That is the most important thing that has been said in the whole forum. Almost all carbs come with a 6.5 numbered Power Valve. That is for Engines with 13 inches of Vacuum or more. Having a power valve too big for the amount of Vacuum the Engine has will keep the Engine in an Over Rich Condition all the time. If you have only 10 inches of Vacuum you need a number 5 Power Valve. This will cure the over rich condition and allow you to fine tune the engine and find the right Jets and Enrichment settings. By the way, it’s a lot easier to adjust the carb using a Vacuum Gauge which is also very helpful in finding the best timing setting. Just remember that on any Engine divide the Vacuum Reading by Two and that is the size Power Valve to use. 12 or more inches use a 6.5, 7 inches of Vacuum use a 3.5.

Most of the time, not necessarily always. If the Engine is in good condition the Vacuum is dependent on the size of the Cam used. The lift is not so important but a lot of Duration takes away Vacuum. This is a very important part of tuning